In the opening episode of "Legends," set in 1990, the story unfolds with the tragic deaths of two young lives. A 15-year-old boy in Liverpool overdoses on heroin, and a cabinet minister's daughter at Oxford University also dies from a drug overdose. The news spreads across the country, sparking a national crisis.
Enter Angus Blake, the Director of Investigations for Her Majesty's Customs, summoned to meet the Home Secretary. The Home Secretary tasks Angus with a daunting challenge: to solve the heroin smuggling crisis in England within six months and with complete freedom. He warns that Prime Minister Margaret Thatcher will soon declare the drug crisis a national emergency, and Angus is ordered to prevent drugs from entering the country.
After the meeting, Angus shares the Home Secretary's orders with Don Clark, the head of operations at the customs office. Meanwhile, customs officers from across the country are summoned to volunteer for this top-secret project.
The volunteers gather at the Customs Office in London, where they learn about a highly confidential investigation and a three-week training program. Angus tells them they will only learn about the investigation if they successfully complete the training. The volunteers return home to say goodbye to their families. Guy talks to his wife Sophie about the opportunity, and she supports him, urging him to make the choice on his own.
The next day, Guy and the other volunteers are taken to a secluded cottage in Yorkshire, where they are not even allowed to contact their families during the training period. Inside the facility, Don teaches the volunteers about data collection and explains how their skills as customs officers can help in this mission. Don is impressed by Erin's data comprehension skills.
The volunteers also learn how to pick locks, and Don notices Kate's determination despite struggling at first. He trains them to think on their feet and is impressed by Bailey's ability to trick people into revealing personal information. The training program pushes them to their limits, but each volunteer brings unique skills and determination to the table, setting the stage for an intense and thrilling investigation that will change the course of England's drug crisis.
When Don spots Guy lurking in the shadows, he dispatches him to a warehouse for an undercover mission, designed to test Guy's mettle. He charges Guy with the task of identifying the distributor of a new drug called ecstasy and tracing its origins. Guy arrives at the warehouse and attempts to lure the dealer into a trap, only to be arrested by a pair of cops who begin searching him for drugs. In a sudden outburst of anger, Guy punches the officers, leading to his incarceration. The other cop pressures Guy to reveal his true identity as an undercover customs officer, but Guy remains silent. Don later arrives and reveals that the entire situation was a test. The cops were sent there to see if Guy would reveal himself as an undercover officer. Don informs Guy that he will be working independently and warns him that he needs to be prepared to lose a lot.
After a three-week training program, Guy, Kate, Erin, and Bailey are the only volunteers remaining. Don shows them a video of Margaret Thatcher declaring heroin a national crisis and asks the four of them to prepare for an upcoming undercover mission. The next morning, Guy, Bailey, and Kate are taken to a secret location that will serve as their new headquarters. There, they reunite with Angus, Don, and Erin.
Erin explains the escalating heroin crisis in England and identifies Liverpool and London as the two cities importing the highest quantities of drugs. Don reveals that Erin will provide logistical support while Guy goes undercover in London and Kate and Bailey do the same in Liverpool.
Angus is deeply concerned about sending Guy to London alone, yet Don insists on his trust in Guy's abilities. That evening, Guy reads a bedtime story to his daughter and says his final goodbyes. He gives Sophie a secret phone number, a safety net she can use to reach him in case of an emergency.
The next day, the trio arrives at headquarters to gather burner phones and other necessary resources for the mission. Guy moves into the rented apartment and begins to follow the mysterious Turks in London. He quickly realizes how secretive they are about their business, witnessing them violently beating up an outsider who tries to trade in their territory.
At headquarters, Guy shares his findings with Angus, Don, and Erin. He explains how difficult it will be to infiltrate the gang without help from an insider. Angus introduces him to a prisoner named Mylonas, who explains that the Turks and the Greeks are rivals. Despite being Greek himself, Mylonas claims to be close to the Turks. He warns Guy that dealing with the Green Lanes Turks is dangerous, but Guy refuses to back down.
Meanwhile, in Liverpool, Bailey and Kate are on a stakeout when they notice young boys chasing them on bicycles. Bailey explains that the kids are spotters before driving away. Later, Kate notices a bread van making multiple rounds through the area and asks Bailey to follow it, though he is skeptical.
In London, Mylonas is released from prison on parole and takes Guy to a bakery, where he threatens to shoot a man over unpaid money. Guy is shocked by the confrontation, but Mylonas later takes him to meet the Turks.
At a club, Mylonas asks to see a man named Hakan, but Hakan's assistant Zeki claims that he is unavailable. Mylonas leaves Guy at the bar and promises to return the following night.
That night, the Turks break into Guy's apartment and interrogate him. Guy responds confidently, recalling Don's lessons about legends - the undercover identities agents must completely believe in order to convince the people they infiltrate. The Turks search through Guy's belongings and threaten to shoot him.
Meanwhile, Kate and Bailey see a man leaving the bread van. At the same time, Mylonas meets the man who was seen at the bar while Zeki is about to discover the letter from Guy's daughter as the episode comes to an end.
